AD-Ai29 453 MODELING OF ELECTROKINESIS(U) ARMY ENGINEER WATERWAY S i/EXPERIMENT STATION VICKSBURG MS GEOTECHNICAL LABJ B WARRINER ET AL. SEP 82 NES/MP/GL-82-i3

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MISCELLANEOUS PAPER GL-82-13

MODELING OF ELECTROKINESISby

v14 James B. Warriner, Perry A. Taylor

Geotechnical Laboratory__ U.S. Army Engineer Waterways Experiment Station

P.O. Box 631, Vicksburg, Miss. 39180

September 1982Final Report

Approved For Public Release; Distribution Unlimited

C..)Prepared for Assistant Secretary of the Army (R&D)Department of the Army

Washington, D. C. 20315

Under ILIR Project No. 4A161101A91D, Task A2Work Unit 141

ILI - -

L4 Destroy this report when no longer needed. Do not returnit to the originator.

The findings in this report are not to be construed as an officialDepartment of the Army position unless so designated.

by other authorized documents.

* The contents of this report are not to be used foradvertising, publication, or promotional purposes.Citation of trade names does not constitute anofficial endorsement or approval of the use of

such commercial products.

w

UnclassifiedSECURITY CLASSIFICATION OF THIS PAGE (ften Date Entered)

READ INSTRUCTIONSREPORT DOCUMENTATION PAGE BEFORE COMPLETING FORM

1. REPORT NUMBER 2. GOVT ACCESSION NO. 3. RECIPIENT'S CATALOG NUMBER

Miscellaneous Paper GL-82-13 ...4. TITLE (and Subtitle) 5. TYPE OF REPORT & PERIOD COVERED

MODELING OF ELECTROKINESIS Final report

6. PERFORMING ORG. REPORT NUMBER

7. AUTHOR(s) 6. CONTRACT OR GRANT NUMBER(@)

James B. Warriner - SPerry A. Taylor

9. PERFORMING ORGANIZATION NAME AND ADDRESS 10. PROGRAM ELEMENT, PROJECT, TASK

U. S. Army Engineer Waterways Experiment Station AREA & WORK UNIT NUMBERSGeotechnical Laboratory Project 4A161101A91D,

P. 0. Box 631, Vicksburg, Miss. 39180 Work Unit 141

11. CONTROLLING OFFICE NAME AND ADDRESS 12. REPORT DATE a

Assistant Secretary of the Army (R&D) September 1982

Department of the Army IS. NUMBER OF PAGES

Washinnton. D. C. 2015 5614. MONITORING AGENCY NAME Y ADDRESS(If different from Controllng Office) 1S. SECURITY CLASS. (of thl report)

UnclassifiedISa. DECLASSIFICATION/OOWNGRAOING

SCHEDULE

16. DISTRIBUTION STATEMENT (of ti l Report)

Approved for public release; distribution unlimited.

17. DISTRIBUTION STATEMENT (of the abetr ect etered In Block 20, It different from Report)

IS. SUPPLEMENTARY NOTES

Available from National Technical Information Service, 5285 Port Royal Road,Springfield, Va. 22151

I. KEY WORDS (Continue on reverse aide if neceoamy ind Identify by block number)

Electrokinetic effects Water flowGeological investigations Water properties

Mathematical models

2&O.7mthACT (C.ae-- severe ab N r-e.. mod idetity by block nmber)

Electrokinetic streaming potentials were measured in typical geologicalmaterials using specially constructed apparatus to model water flow throughsubsurface flow paths.

The apparatus used for the study is described by this report as are themeasurement techniques used. Comparisons between the observed electrokinesisphenomena and theoretical predictions are made. (Continued)

D O 103 oIvow oF ovesisogOLETf Unclassified

SECURITY CLASSIFICATION OF THIS PAGE (When Date Entered)

U --

UnclassifiedSECURITY CLASSIFICATION OF THIS PAGE(Whm Data Entet.4)

0. ABSTRACT (Continued).

Conclusions resulting from this study include:-

a.,, Studies of streaming potentials in typical geological materials sh, ildbe concentrated in real geological environments;

b.' Fluid electrical resistivity as influenced by dissolved ion contc '

more critical to streaming potential measurements than temperatuifluences and should be measured directly,.'

c. Contrary to the results of past studies of streaming potentials, it wasfound that metallic electrodes performed more satisfactorily than didnonpolarizable porous pot electrodes:

d. A relationship was observed between the flow rate of the water through .

the porous media and the electrical surface potential of the solid

portion of the media. This relationship may provide a useful applica-tion of streaming potential surveys after further development/ ,4,,

e. The presence of appreciable amounts of clay in or near the water flow

path through porous media degrades electrokinetic potential magnitudesand hinders streaming potential measurements.-- - S

.A

V V

U S

V UqW

Unclassified

SECURITY CLASSIFICATION OF THIS PAGEftPe Daa Entered)

DV

PREFACE

The study reported herein was performed under the In-house

Laboratory Independent Research (ILIR) Program, Project Number

4AI61101A91D, Task Area 02, Work Unit Number 141, entitled "Field Model-

ing of Electrokinesis." Mr. F. R. Brown was the WES Technical Monitor.

The investigation was conducted by the U. S. Army Engineer Water-

ways Experiment Station (WES) during the period FY 80 - FY 82. The

study was conducted under the direct super--iFion of Mr. J. S. Huie,

Chief, Rock Mechanics Applications Group (RMAG), Geotechnical Laboratory

(GL), and under the general supervision of Dr. D. C. Banks, Chief, 'V

Engineering Geology and Rock Mechanics Division (EGRMD), CL. Dr. W. F.

Marcuson III was Chief, GL. Mr. J. B. Warriner, RMAG, prerared the

report with the assistance of Mr. P. A. Taylor, RMAG. Mr. Taylor de-

signed and constructed the experimental models and he and Mr. L. R. r *Flowers, RMAG, conducted all measurements.

Commanders and Directors of the WES during the investigation and

preparation of this report were COL Nelson P. Conover, CE, and

COL Tilford C. Creel, CE. Technical Director was Mr. Fred R. Brown. r

- C

?HTI3 IA&D T I C T A .Uaa33aounes.

~~Ditribtion/ ,

DI val I

1

-5

CONTENTS

PREFACE . . . . . . . . . . . . . . . . . . . . . . . . . ..

CONVERSION FACTORS, U. S. CUSTOMARY TO METRIC (SI)UNITS OF MEASUREMENT . . . . . . . . . . . . . . . . . . . . .

PART I: INTRODUCTION . . . . . . . . . . . . . . . . . . 4

Background . . . . . 0 . .. . . .. .. . . . . . . . .. 4Purpose . . . . . . .0 0 . . . . . . 0 . . . . . . . . . 4Scope . . .0 . . . . . . . . . . . . . . . . . 5

PART II: LABORATORY STUDIES .................. 6

General Review . . . . . . o . . . . . . ... . 6Model Development . .................... 10Box FlowModel . . . . . . . . . . . . . . . . . . . . 11Pipe Flow Model . . o o o . . . . 0 . . . . . . . . . * 15

PART III: RESULTS . o . . . o . . . . . . . . . . . . . . . . . 18

Electrode Testing and Evaluation . o . . . . . ... . .. 18 ULarge Parallelepiped (Box) Flow Model . o o . . . ... . . 19Plastic Tube (Pipe) Flow Model ............... 26

PART IV: CONCLUSIONS AND RECOMMENDATIONS o . o .. . . . . ... 30

Conclusions . o . . . . . . .. . . . . .. .. . . .. . 30Recommendations . . . . . . . . . . . . . . . .. .. . . . 31

REFERENCES o o o a e e o o o o o o o a e e o o e o 33

TABLES 1-5

FIGURES 1-17

S .

S S

2g

I U

CONVERSION FACTORS, U. S. CUSTCMARY TO METRIC (Si)UNITS OF MEASUREMENT

U. S. customary units of measurement used in this report can be con-

verted to metric (SI) units as follows:

Multiply By To Obtain

feet 0.3048 metres U

gallons (U. S. liquid) 3.785412 cubic decimetres

inches 2.54 centimetres

square feet 0.09290304 square metres

W SU W

p. -

p . ,

3

.p

MODELING OF ELECTROKINESIS

PART I: INTRODUCTION

Background

1. The study reported herein consisted of a series of laboratory V

experiments intended to delineate major factors affecting the applica-

tion of electrokinesis measurements to the location of water seepage

paths. Electrokinesis is a term defined as relating to the motion of

particles or liquids that results from or produces a difference of elec-

tric potential. The term electrokinesis has generally been applied to

phenomena observed under laboratory conditions. When electrical poten-

tial surveys have been performed in the field for the purpose of de-

* scribing the flow of subsurface water, the term "streaming potential"

has been used to describe the same causative phenomenon as

electrokines is.

2. In 1979 an In-house Laboratory Independent Research project

was proposed and approved. That proposal was made to assist in develop-

ing the U. S. Army Corps of Engineers (CE) capabilities to locate and

describe subsurface paths of water seepage from reservoirs. The work

was intended to result in field-usable geophysical survey techniques.

* The study had been in progress for several months before it was learned

that an independent, separately sponsored effort wvs being carried on by

personnel of the Earthquake Engineering and Geophysics Division (EEGD)

that had been successful in emplacing a streaming potential measurement

system at Gathright Dam, Virginia. The present study was reoriented at

that time (1980) toward examining the factors affecting the magnitudes

of measured streaming potentials.

* Purpose

3. The purpose of this report is to describe a laboratory study

of the phenomenon known variously as "streaming potential" or

4

I U 5

"electrokinesis." The present study was performed under laboratory con-

ditions on a large scale to simulate the occurrence of electrokinesis in

typical geological materials. The intent of the study was to "bridge

the gap" between an understanding of electrokinesis as it is observed in

the laboratory and as it is observed in field surveys.

ScopeI lis

4. This report will present a background of electrokinesis as

studied in the past. Brief descriptions will be given of the study

methods proposed and used. The results obtained will be presented. The

conclusions of the study will be presented.

P 1

5 .. . . ...

PART II: LABORATORY STUDIES

General Review

5. Electrokinesis is defined as the electrical potential devel-

oped by the motion of some fluids flowing under pressure head over cer-

tain solid materials. The phenomenon is best observed when the flow is

through narrow conduits within the solid material, e.g. the interconnec-

ted pore spaces of a porous granular medium. Electrokinesis was first

observed by Helmholtz and reported by him in 1879 as it occurred when

water was passed through a column of primarily quartz sand under

pressure. Electrodes implanted within the sand developed an electrical

potential which varied according to the pressure head applied to the

flowing water. The expression describing the electrokinesis phenomenon

as given by Smoluchowski (1951) is:

AEp = D fl C Kf 1)l

where

AE measured streaming potential (electrostatic volts)spP - applied pressure head (cm of water)

D dielectric constant of water (dimensionless)fl

-surface potential of solid medium (electrostatic volts)

- viscosity of water (poise)

Kfl M specific conductance of water in flow channels (mho/cm)

6. The following is a qualitative description of the cause of

*g streaming potential. Water possesses an electrically dipolar molecular *

structure in that the two hydrogen (positive charges) atoms are not dia-

metrically opposed on the oxygen atom. They are, instead, at a relative

angle of III deg to each other. Therefore, each molecule of water has a

* positively charged region (oriented between the positive hydrogen pair)

and a diametrically opposed negatively charged region (oriented toward

the negative oxygen atom). Many natural solid media possess a molecular

structure in which the surface of the solid is characterized by negative

6

U - -- - - - - - -

electric charges. Among these natural media with negative surface elec-

tric potentials are silica-based mineralogies and carbonates. Electro-

static attraction between the negatively charged grain surfaces and the w -.

positively charged pole of the water molecules causes a layer of water

to affix itself to the grain surfaces leaving, in turn, a more weakly

negatively charged region exterior to that first water layer. In non-

flowing water-solid systems the thermal motion inherent to the individ-

ual water molecules prevents more than two layers to be electrostati-

cally bound to the grain surfaces; hence the descriptive term "Water

double layer" is applied. If, however, the water phase of the system

exhibits directional flow under a pressure gradient, then some molecules .W

of the more weakly bound outer layer of molecules are swept away. The

electrostatic charge imbalance that remains near the solid grain sur-

faces is negatively charged and is observed as an electric potential.

That potential, represented herein as AE SP, is the "streaming" or

"velectrokinetic" potential.

7. As described by Equation 1, the streaming potential is propor-

tional to the pressure head applied to the water. The streaming poten-

tial is directly proportional to the dielectric constant of the water,

D *The dielectric constant of a polar liquid in an electric field isfia measure of the force applied to components of that liquid by the field

(Carson and Lorraine, 1962). The surface potential, ior "zeta"ls

potential represents the strength of the solid grain surface electric

field. The viscosity of the water represented in Equation 1 partially

governs the nature of flow through the pore spaces between the solid

grains. The specific conductance to electricity of the fluid in the

pore spaces (inverse of specific electrical resistivity, K fl- l/P f)governs the streaming potential by defining the intensity of electric

potential difference from point to point that can remain in equilibrium

(Carson and Lorraine, 1962).

8. Much of the laboratory study of streaming potential has been

oriented toward explanation of the "self-potential" or "SP logs per-

formed routinely with the single-point electric logs in borehole geo-

physical surveys. The self-potential log is a passive measure of

7

W

electric potential measured continuously up boreholes relative to a

surface grounding probe. Movement of water between a borehole and the

surrounding geologic strata can arise because of (a) osmotic pressures

tending to balance dissolved salt concentrations between the mud column

* and the formation fluids, or (b) because of hydrostatic pressure differ-

entials between the mud column and the natural piezometric pressure, or

* (c) because of water movement across interfaces between different

formations. Motion of the water, regardless of cause or orientation,

develops an electrokinetic streaming potential which is the basis of the

SP log. Bull and Gortner (1932) studied the effect of grain size on the

electrokinetic potential. They found no linear relationship betweenlopressure and the streaming potential when the quartz grains were of het-

erogeneous size mixture but did find a good relationship ( A~E .1/3

where is a grain diameter) for a homogeneously sized quartz

aggregate. Wyllie (1951) examined drilling mud samples flowing through

Uw U

their own filtrates to separate the component of the cross-mud cake

streaming potential from the self-potential log. Schriever and Bleil

(1957) determined that the ratio AE /P did not vary with the config-sp

uration of the quartz sand flow systems they studied, including the

length of the columns of sand. Condouin and Scala (1958) reexamined

streaming potentials originating in the borehole mud cake and measured

appreciable streaming potentials across shale samples in their

laboratory. Bernstein and Scala (1959) studied streaming potentials at

the interface separating two electrolytic solutions and also verifiedi

their existence and positive sign in shale samples..

9. A second area in the study of streaming potentials has been

their relationship to the galvanic corrosion of metallic well screens.

Mandal (1969) and Mandal and Edwards (1971) measured streaming poten-

tials generated by water flowing through clean quartz sand between

metallic screens. They measured the quartz zeta potential (using tap

water), as -1250 my and determined that screen incrustation could be

initiated by the streaming potential. Theirs is the only experimental

value for the natural grain surface potential.

8

U, -- - - - - - - - -sp

* ~ ~ ~~~ - - - - - - - - -

10. A third area of past study of the streaming potential phenom-

enon has been its application to surface-based surveys to delineate sub-

surface paths of water seepage. Ogilvy, Ayed, and Bogoslovsky (1969)

described a series of measurements in their laboratory and in two im-

pounded reservoirs that used streaming potential values, water flow rate

observations, and thermometry to locate paths of leakage from those

reservoirs. Their laboratory studies were made using clean graded

quartz sand in a glass flow tube through which various solutions of

electrolytes were passed at controlled pressure heads. Their results

from laboratory tests were as follows: with increase in permeability

the ratio AE /P increases to a maximum near k - 60-70 darcy (wheresp

k is the permeability to water) and then decreases to a constant value;

AE Ip P decreases with increasing electrolyte concentration (increasing

electrical conductivity). They conIclude that the process must occur

under laminar flow conditions and "is apparently violated when the flow

is turbulent, which takes place in rubble and big open fissures when the

gradients are high." Ogilvy et al. (1969) caution, also, that the pres-

ence of clay in even part of the rock fissures will lead to positive

values of streaming potentials as great as or greater than the negative

potentials generated in clean fissures in rock. No differentiation was

stated between streaming potential as it occurs in a silica-based

geology as opposed to a carbonate geology. Ogilvy et al. (1969) dragged

nonpolarizable potential electrodes along the reservoir bottoms to pro-

duce a series of traverse measurements of streaming potential. The

electrodes were in the form of porous ceramic cylinders containing lead

chloride coated electrodes immersed in potassium chloride solution. At

one reservoir on "tuffaceous geology," leakage zones were identified by

negative potential regions under the reservoir and the "amplitude of the

anomaly indicates the intensity of leakage." However, distortions in

the streaming potential measurements were seen to be caused by formation

W contacts, by clay concentrations in joints, and the presence and thick-

ness of bottom mud. The interpreted investigations indicated -20 to

-40 my streaming potentials were correlated with four leakage zones

through joints in basalt that flowed at 50 to 100 mm/sec. At the second

9

-.

reservoir in quartzose conglomerate similar instrumentation was used and

-10 to -30 my streaming potential anomalies were correlated to leakage

rates of 6-20 mm/sec. Positive electrical potential measurements in the

latter survey were interpreted as the result of "lithologic

peculiarities." Bogoslovsky and Ogilvy (1970) described a further

application of streaming potential measurement to quantifying the rate

of flow through leaky zones of reservoirs.

11. Applications of streaming potential surveys to seepage path

location have been recognized by the Corps of Engineers since before

1972. A study at Walter F. George Reservoir in the South Atlantic Divi-

sion was performed under contract using streaming potential measurements-3

(Saucier 1970). Bates (1973) referred to streaming potential surveys as

a possible search strategy for locating subsurface cavities. EM 1110-2-

1802 (Department of the Army, Office, Chief of Engineers 1979) refers to

streaming potential surveys as a potentially valuable geophysical method.

Most recently the Earthquake Engineering and Geophysics Division (EEGD)

of the WES has undertaken concept trial surveys at Gathright Dam,

Virginia, and Clearwater Dam, Missouri (Cooper, Koester, and Franklin

(1982) and Butler, Llopis, Koester, and Kean (1981)). The method of the

surveys conducted by the EEGD has been to install semipermanent elec-

trodes in traverses transecting geologically probable seepage paths

which incorporate both intact and leaky zones. After obtaining a series

of electrical potential measurements for comparison purposes from the

individual electrodes comprising the transection, a series of perturba-

tions were applied to the water flow regime in the form of increased

pressure heads or electrical fluid conductivity changes or both.

3Model Development

12. In modeling the flow of water through an aquifer a large rec-

tangular box was first used. The box was made of wood and sat on level

ground. Water seeped from the flow channel to the outside ground. Be-

cause of the many hydraulic and electrical flow paths to the ground, the

q 110

qV

* -.

box was unsatisfactory as a model. A 3-i/16-in.* ID 2-ft-long plastic

*polyvinyl chloride (PVC) pipe was used to eliminate the different elec-

trical flow paths to ground. Both of these models will be described as

well as the technique used to run the tests on each model.

Box Flow Model

Box construction

13. A box was constructed of 3/4-in. waterproof plywood with in-

side dimensions of 12 ft long, 4 ft wide, and 4 ft high. Centered at

the bottom on each end was a distribution plenum which was rigidly con--W

nected and sealed to the box. The two plenums were 4 in. long, 1 ft

wide, and 1 ft high (length, width, and height are in the same direc-

tions as the large box dimensions). Each plenum contained the water

port from the outside, and the 1-ft x 1-ft interior face plate of the

plenum contained many holes allowing water to flow evenly into the

sample. The modeled flow channels were 1 ft x 1 ft in cross section and

extended the length of the box from plenum to plenum. See Figure 1 for

details of the box construction.

Hydraulic system

14. The hydraulic system was designed to allow water to flow

through one end of the box through the plenum and the 1-ft cross sec-

tion along the full length of the box into the other plenum and out of

*I the box to an overflow with variable height capability. Manifolds and

valves were used to reverse the direction of flow. Piezometers moni-

tored the water pressure at different points in the system.

Water supply

15. The water supply was a 55-gal drum connected to a U. S. Army

Engineer Waterways Experiment Station (WES) waterline. The drum sat on

an elevated platform. At the bottom of the drum a manifold made of

1-in. pipe fittings was connected to allow water to be supplied to ei-

ther plenum. A piezometer, made of 3/8-in. clear Tygon tubing, was

* A table of factors for converting U. S. customary units of measure-

ment to metric (SI) units is presented on page 3.

11

placed vertically on the side of the barrel and a scale placed behind it

and used for measuring water levels to + 0.01 ft.

* North-south inlets and outlets

16. The water leaving the manifold of the water supply flowed to

* either end of the box where valves allowed water to enter the box and

plenum or go out of the overflow. If the water was to enter the mani-

fold at one end, the overflow for that end was shut off. The water

flowed through the first plenum, the sample, the second plenum, to the

manifold on the other end where the inlet valve was closed and the over-

flow valve was open. If flow was desired in the opposite direction all

valves positions were reversed. Open-tube piezometers were used to

measure the head in the plenum at either end of the box.

17. In order to measure flow rates, the overflow pipe protruded

through the bottom of a steel cup that had a V-notch cut into its side.

A bill was welded to the V-notch, directing the discharge water to fall

into containers of known volume for measured periods of time. The over-

flow cup was mounted on a bracket which slid vertically in a slot to ad-

just the elevations of water entering or leaving. The cup had a refer-

ence scale fixed to one side of the slot and calibrated simultaneously

with the piezometer scales by filling the empty box to a known water

depth and then setting all of the scales to the same reading. The bot-

tom of the box was defined as zero elevation.

* Sample

18. Initially, the samples were either sand or pea gravel in a

"flow channel" surrounded by soil. The pea gravel was found later to be

too coarse and sand was used exclusively. The grain size analyses for

the sand and gravel are shown in Figures 2 and 3, respectively.

19. The samples were formed by placing rigid 1/16-in. x 12-in. x

13-in, steel sheets into parallel grooves in the floor between the

plenums. The sheets were placed end to end for the full length of the

W box. A thin lift of aggregate was placed between the two rows of metal

and the soil, loess, placed on the outside of each row of metal sheets.

It was important to place the soil outside the sheets for each layer of

aggregate in order that support be given to the tin sheets and ensure a

12

constant 1-ft 2cross section of sand along the length of the box. A

thin filter cloth was placed in front of each plenum, on the floor under

the samples, and on both sides with a flap left to cover the top of the

* sample as a single sheet. After the sample was placed to its full 1-ft

depth the metal plates were removed, leaving a sand channel between two

soil channels of equal height. Soil overburden was then compacted in

* . place. Figure 4 shows the completed sample configuration.

20. To determine the electric potential caused by the flowing

water, probes had to be chosen which would minimize electrical self-

potential. Self-potential of probes is caused by galvanic reactions of

I IN dissimilar metals in an electrolytic fluid. Probes were designed and

tested as follows: a copper wire was placed inside a 1/8-in. OD Tygon

tube and an aquarium filter was filled with copper sulfate powder and

connected to the tubing (Figure 5). The wire was forced into the filter.

The Tygon tubing was filled with a saturated solution of copper sulfate.

When pairs of these probes were placed in water, the potential differ-

ence between the probes was found to be greater than that expected for

streaming potential. The self-induced voltage made these probes useless

for measuring streaming potentials.

21. A second type of probe was then designed (Figure 5). The

copper wire was replaced by coaxial cable. The cable was stripped back

1/2 in. to expose its center wire with insulation intact. The insula-

tion on the center wire was trimmed back 1/4-in. A piece of silver sol-

- der wire 4 in. long was soldered to the 1/4-in, stub of the center wire.

A plastic sheath covered all but 1/2 in. of the silver solder at the

bottom and extended 1 in. above the coaxial cable splice. The sheath

was then filled with silicone sealer and allowed to dry. Two of these

cables were made 20 ft long with a coaxial connector attached to an alu-

minum junction box which linked the two coaxial shields together. The

wires were shielded in order to eliminate any stray electric potential

in the air. After placing the probe tips in water it was noted the ob-

served stray potentials picked up by the exposed and unshielded central

conductors disappeared. Additionally, these electrodes cost very little

to make and were more durable than the fragile porous pot electrodes.

13

Detecting streamingpotential using the box model

22. The depth of compacted soil cover over the flow channel de-

termined the maximum possible hydraulic head to be established by a cri-

terion that the overburden pressure not be exceeded. The hydraulic head

was set low at first and increased to maximum head for the following

tests. The head differential was controlled by two variables: the ele-

vation of the water in the supply barrel and the elevation of the over- '

flow cup at the discharge end of the box. After several preliminary

tests it was concluded that for a series of tests the overflow should

remain at a constant elevation and the differential head should be regu-

lated by the water elevation in the supply barrel. After setting the

head, 5 to 10 min was allowed for equilibrium before measuring the time

required to fill a volumetric container. Three measurements were made

of the flow rate and the flow was assumed to be in equilibrium if the

W times did not vary more than 0.5 sec.23. After the flow was judged to be stable, five parameters were

recorded for each test in a series. First, the three piezometers were

read, being (a) the water supply, (b) the north, and (c) the south end

of the box. The fourth parameter was that of the elevation of the

overflow. The fifth and final measurement was that of the electrical

streaming potential measured by a high impedance (greater than

50 megohms) digital multimeter. The differential head was then in-

creased and the measurements repeated until the maximum head was reached

or the box flooded with water.

24. One of the main problems encountered in the test was insta-

bility in the readings. It was found that the loess soil was piping to

the surface and through holes in the box. Because of the changing paths

for the flow of water and electrical current the box model was judged a

* failure as far as this experiment was concerned.

14

V - - -- - - - - - 1

Pipe Flow Model

-, 25. The instability in voltage readings encountered with the box

flow model was thought to be caused by multiple water flow channels and

electrical current paths. There was concern about stray currents caused

by radio, television, and industries as well. The pipe flow model was

designed and built to eliminate as many variables as possible.

Pipe model construction

26. To keep variables to a minimum the pipe model was simple.

The tubular flow cell was a 4-in. OD, 3-1/16-in. ID PVC pipe 2 ft long.

Holes were drilled and tapped for 1-in. water pipe in the center of two

PVC caps which covered the ends of the PVC pipe. The same manifolds

used on either end of the box model were removed and screwed into the

caps of the pipe model; 5-29/32 in. from the center in either direction

down the length of the pipe holes were drilled and tapped for 3/8-in.

pipe thread. A 3/8-in. hole was drilled through the center and down the

entire length of two swaged pressure fittings. A hard plastic sheath

5 in. long and 3/8-in. OD was glued over the probes described in para-

graph 21, leaving only the 1/2 in. of electrode tip exposed. The al-

tered ferrule fittings were screwed into the two 3/8-in.-diam holes and

the two potential probes could be inserted and removed through these

watertight fittings. A cylinder of aluminum wire screen was fabricated

to encircle the pipe model and the wire on the coaxial shield was con-

nected to both it and the ground to minimize electrical interference.

The pipe model was cradled horizontally in wooden brackets. See

Figure 6 for details of the pipe model.

Hydraulic system

27. The water supply plumbing for the pipe model was the same as

the water supply for the box model with a few exceptions. The water

supply barrel was elevated higher to allow greater pressures in the

completely sealed sample container. The heads were read by open-tube

piezometers as in the box test.

28. Flow through the two manifolds was similar to that of the box

model. The water was supplied from a WES waterline. Water flowed

15

w - - -

through a 1-in, water pipe either to the left or right end of the pipe

model. The water then flowed through the sample in the pipe and out the

overflow. In the pipe model the water flowed through a filter cloth at

both ends of the cell. The water entered the pipe model, passed through

the first filter, continued through the sample, through the second fil-

ter and out of the pipe, and through the manifold to the overflow at the

opposite end.

Test procedure

29. Measured data were: supply head, discharge water tempera-

ture, time of the reading, three 6eparate volume-per-unit time measure-

ments, specimen electrical resistance, probe 1-to-ground voltage, and

probe 2-to-ground voltage.

30. The typical test procedure described will be that used for

the sand specimen. The pipe model was removed from its cradle and both

caps removed. A filter was placed in one of the caps and the cap put

back in place over the end of the pipe. The open end of the pipe was

held up to the vertical position. Lifts of 4 in. each were placed in

the pipe and the pipe vibrated to make the sand more dense or compacted.

This procedure was continued until the pipe was completely full and the

sand molded to fit inside the other cap. A filter cloth was placed in

the other cap and it was placed on the end of the pipe. The probes were

inserted and sealed to the pipe and the cylindrical screen shield placed

around the pipe. The pipe was placed back in the cradle and the water

pipes connected. The same procedure was followed for the crushed lime-

* stone tests and the test using sand and soil together.

31. With the supply set at a desired head the valves were set to

allow water to flow from left to right, for example, and the time and

temperature recorded. As water began to flow from the barrel, the water

supply was regulated to maintain a constant water level in the barrel.

After the water level was regulated the flow was checked using precision

volumetric flasks and timed intervals. Flow tests were repeated until

two successive measurements agreed within 0.5 sec after which three re-

corded flow measurements were made and averaged. The electrical resist-

ance of the water was read by a 1000-Hz ohmmeter through the two

16

W"

electrodes on the center line of the model cell. Voltage 1 and

voltage 2 were then recorded bet Ren the probe on the right end of the

pipe and a ground wire and the vcltage between the probe on the left end

of the pipe and a ground wire, respectively. Both of the voltages were

read by the digital multimeter.

32. The minimum head in feet observed by trial and error tc be

capable of maintaining constant flow was subtracted from the maximum

head that the system was capable of providing and this number divided in

order to have ten tests increasing by equal increments. These ten tests

constituted a series of tests after completion of which the direction of

flow was reversed and another series of tests performed. After a series

of tests in each directions, a different sample was prepared.

P

P

P

17

UV

PART III: RESULTS

Electrode Testing and Evaluation

33. The initial attempts at developing electrodes were based upon

recommendations given in Ogilvy et al. (1969), in Jakosky (1950), and

other references. Without exception, the recommended electrode type for V

any electrical potential survey was the "porous pot" electrode. Elec-

trical connection in such an electrode is made by means of a metallic

electrode immersed in an aqueous solution fully saturated with a salt of

that electrode metal. The electrolyte is contained in a porous nonme-

tallic vessel which is, in turn, fully saturated with the electrolyte

solution. The porous pot is placed in contact with the ground and the

entire assembly is treated as the measuring electrode. The intent of

using porous pot electrodes is to minimize galvanic and electrolytic

polarization potentials generated by contact of dissimilar metals, dis-

similar solutions, or metal-to-soil contact.

34. The porous pot electrodes, intended to be electrically nonpo-

larizing, were assembled in pairs and tested by using a high-impedance

(50 megohm) digital multimeter between the two electrodes while they

were immersed in a bath of tap water, which would be the fluid used in

the streaming potential tests. Each pair tested was left immersed in

the water bath for at least 24 hr before the self-generated electrical

potential was measured between them. The immersion period was intended

to allow temperatures and osmotic pressure gradients to stabilize. An

immediate potential difference between tested electrode pairs of +12 to

-60 mv was measured. Of the six electrodes fabricated, all combinations

of pairs tested demonstrated the excessive self-potential. The stabili-

zation period was varied between 5 min before measurement and 48 hr but

the immediate self-potential values showed no correlatable pattern in

magnitude or electrical sign. A pair of electrodes was observed contin-

uously by voltage measurement for a period of 4 hr. The potential var-ied from :12 rv to +134 mv after 30 min and then decreased to +39 mv in Ithe next 2 hr. The potential had risen again to +73 mv when the series

V]

18 -

"-1

of measurements was halted. Despite provision of continuous electrolyte

replenishment, constant temperature control, and electrical connection

quality checks, the porous pot electrodes as constructed and tested -0

never demonstrated electrical stability.

35. Bare silver wire electrodes were used as an expedient control

test to differentiate between the effects of using tap water as the

* measurement fluid and possible electrical instabilities inherent to the -

porous pot electrodes as constructed. Silver was chosen because it was

readily available in the form of silver solder and because it is rela-

tively inert in aqueous solutions as compared to copper or lead. In the

first attempt to use the silver electrodes the generated self-potential

* between them in fresh tap water was found to vary slowly between -3.2

and +3.0 my over a period of 2 hr. Repetitions of the measurement se-

* ries, each time using fresh tap water and polished electrodes, confirmed

the observed electrical stability of the silver wire electrodes. -

36. Cooper et al. (1982) reported successful usage of long

copper-c)ad steel electrodes in the Gathright Dam streaming potential

* survey. Butler et al. (1981) reported similar success in using 2-f t-

* long copper electrodes at Clearwater Dam. Based on the above-described

field evidence and this study's finding that minimal electrical self-

* potential was generated by metallic electrodes, the further use of po-

rous pot electrodes was discontinued for this study. No hypotheses are

* presently offered to explain the successful usage of metallic electrodes

- nor the instability of the porous pot electrodes as fabricated. During

the work with the flow models the efficacy of using metallic electrodes

was thought to be fortuitous rather than possibly serendipitous.

q WLarge Parallelepiped (Box) Flow Model

37. A large aboveground model of a soil-confined granular flow

channel was constructed as described in paragraph 13. The flow channel

* was a parallelepiped with flow along the longest dimension. The granu-

lar medium was placed in successive lifts of approximately 2 in. to a

final depth of 12 in. concurrently with placement of the loess soil

q U

19

- - -- - - - - - - -

confinement on either side of the channel. The silver wire electrodes

were placed by hand as the granular medium and soil lifts were compacted.

The electrodes were each located centrally within the square cross sec- -

tion of the flow channel and 1 ft from the nearest respective water dis-

tribution plenum. After completing the placement of the granular flow

medium further increments of loess soil were compacted in 2-in, lifts

over the flow channel and soil lateral confinements. The granular flow -

medium first placed in the above manner was washed pea gravel of which

90 percent passed a 3/8-in, screen and 98 percent was retained on a

No. 4 screen. The gravel was chosen because its intergranular pore

space dimension (assumed to be approximately 0.25 in.) was comparable to

fracture apertures in jointed rock masses. Gravel was also readily

available. The water supply constant head control was set to coincide

with the elevation of the top of the flow channel and the system allowed

to saturate with water by gravity flow for 24 hr. Open-tube piezometers

at either end of the flow channel and in the center verified that the

flow channel had a zero gradient along its entire length and the water

level in the flow channel was at the top of the channel. The tailwater

elevation control was set at 1.010 ft and the headwater elevation con-

trol set at 1.020 ft for a gradient of 0.010 ft in 11 ft of length (i

0.010/11.0 = 0.0009, where i is the gradient). The discharge rate was

measured by timing the rate of filling of a 0.270-gal container. The

average elapsed time for three successive measurements was 1.577 min and

the resultant discharge rate was

Q Discharge Volume =011 pElapsed Time

Using Darcy's law for flow through porous media

Q -k iA (2)

where

Q - discharge rate (L 3 T)k - coefficient of permeability to water (LIT)

20

i = pressure gradient = AH/A (L/L)

AH = head difference = headwater elev - tailwater elev (L)

Z - length of parallelepiped flow channel (L)

A - cross-sectional area of parallelepiped (L2)

Rearranging gives

k QiAV

and using the above values,

k f 190.2 gpm/ft2

f 12.91 cm/sec

This value of coefficient of permeability from measured values led to -

U

the calculation of Darcy velocity from

v = k i (3)

where

v - Darcy velocity of flow through a parallelepiped of porousmaterial (L/T)

v - (12.91)(0.0009)

- 0.0116 cm/sec

and subsequent insertion in the equation for Reynolds number to charac-

terize the flow as laminar or turbulent (Bouwer 1978):

N w v D50 (4)R =

where

W I N R - Reynolds number (dimensionless)SR3

Yw M density of water at 20C (M/L )

D - average particle size (L)

- viscosity of water at 20°C (M/LT)

21

U

N(0.9982) (0.0116) (0.635)R 0.010

-0.735 -

Using N R< 1.0 as a criterion for laminar flow (Bouwer 1978), the flow

in gravel at a head of 0.01 ft was laminar. Further calculation using

Equations 3 and 4 shows, however, that the criterion on Reynolds number

* would be violated at imposed head differences greater than 0.013 ft.

Despite the prediction a test using a head difference of 0.1 ft was

performed. The test failed due to piping and flushing out of the loess

cover and side constraints. Potential measurements were erratic with

variations exceeding 1000 my. The gravel channel medium was discarded.

38. Washed concrete sand was used next for a granular flow medium

in the large flow model. By visual inspection the sand was at least

U90 percent quartz grains. The average grain diameter (D 50 was V

0.0165 in. The gradation was as follows:

Cumulative percentSieve size weight retained

No. 4 7.3No. 8 16.4No. 16 22.8No. 30 31.2No. 50 86.7No. 100 96.4No. 200 97.3Pan 100.0

Assembly of the flow model was as described above for the gravel medium

4 except that a single layer of filter cloth was placed on both sides and

top of the soil-encased flow channel to retard soil erosion under high-

flow velocities.

39. Water was allowed to flow freely into the buried sand channel

under gravity head equal to the elevation of the top of the sand channel.

The time required for the central open-tube piezometer to indicate a

constant water level along the sand channel was 48 hr. The tailwater

22

elevation control was left stationary and level with the top of the

channel, while the headwater elevation control was raised in 0.1-ft

increments at intervals of 1 hr. A head difference of 0.4 ft of water

was required before the first water began to flow from the tailwater

discharge pipe. The discharge rates varied erratically for several

hours before stabilizing at 8 ml/min measured in a graduated cylinder

(Q - 0.0021 gpm). Using a gradient of i - 0.40 ft/ll.0 ft = 0.0364

and Equation 2, the coefficient of permeability to water was k =

0.0577 gpm/ft2 (= 3.9 x 10- 3 cm3/sec/cm2). The Darcy velocity from

Equation 3 was

v = 0.0014 cm/sec

The Roynolds number from Equation 4 was

N = 0.0009 < 1R

and laminar flow was seen to be probable for all proposed applied pres-

sure heads, thus satisfying a requirement for streaming potential

development.

40. The digital multimeter was connected to each of the buried

electrodes in turn and the reference ground potential point in the soil

outside the model. The reference ground point was not moved as attempts

were made to measure generated electric potentials at the electrodes.

All successive measurements and observations made on a continuous basis

for several minutes varied randomly through a range of about 10 mv with

either positive or negative signs. It was reasoned that an electrolytic

equilibrium or flow equilibrium had not been achieved, and the system

was left in a constant flow condition for three days. During that time

the measured electric potentials did not increase or stabilize. The

flow of water gradually decreased to a zero rate despite verification of

the water supply pressure. To reestablish water flow the headwater

elevation control was raised in increments of 0.1 ft from AH - 0.4 ft

When the head differential approached 1.0 ft, water was flowing from the

23

w

IU -O

tailwater discharge but the soil encasing the flow channel exhibited

signs of complete saturation, heaving and cracking of its surface, and

ultimately the surface became covered by water seeping upward. The

silicone-caulked joints of the box began leaking and the test was halted

without any meaningful electrical data nor establishment of reliably

controlled water flow.

41. The conclusion was that the model concept of encasing a

fairly large aggregate flow channel in remolded soil was not feasible

within the constraints imposed by economical model assembly. Despite

the failure to accomplish a detailed series of electric streaming poten-

tial measurements the initial data obtained before model failure showed

that any measurable streaming potentials were substantially lower in

magnitude than random electrical noise levels of +10 my. Measurements

were made of the electrical resistivity of the water discharged from the

model, the resistivity of the sand aggregate saturated with discharged

water, and the resistivity of the soil from the model saturated with

discharged water. The resistivities were measured using a Lucite cell

with dimensions such that a direct measurement of electrical resistance

through the tested medium is numerically equal to the electrical resis-

tivity in units of ohm-cm. The resistivities were measured on five

samples of each medium and the average values were as follows:

Average electricalMaterial resistivity, ohm-cm 5

Discharge water 5,300Saturated sand 50,500Saturated soil 2,875

From the CRC Handbook of Chemistry and Physics (Weast, Selby, and Hodgman

1965) the dielectric constant of water at 200C, D , equals 80.36. From

Mandal (1969) the surface potential, s , or zeta potential for sand and

tap water equals -1250 mv. The fluid electrical conductivity is obtained

as the inverse of the fluid electrical resistivity:

Kfl -- (5)f fl

24

V - - - - -- -

-

where- fluid electrical resistivity (ohm-cm)

fi

Equation 1 is stated in terms of electrostatic units of potential and V

centimetres head of water. To convert to the centimetre-gram-second

system of measures the following factors are applied:

AE : D /4n U (1 bis)

P fl 5 fl

(8.99 x 1011) g (6)

4 r KYfl

where

g = gravitational acceleration = 980 cm/sec 2

=fl = density of water at 20*C = 0.999 gram/cm3

Inserting values for the soil-enclosed sand channel,

(80.37)(-1250) 1 (980)AE =8.99 x 1011P 0.01 / 1

0. 999) (5300

= 4.61 mv/cm

And for P - 12.92 cm water

A E - -59.6 mv

42. The calculated magnitude for streaming potential, 59.6 mv, is

higher by a factor of 6 than the variations actually observed in the

model test. A possible cause of the measurement failure was determined

to be electrical in nature by conceptualizing the model flow channel as

an electrical battery with one pole at the inserted electrode and the

other at the common grounding point outside the model. The extremely

low resistivity of the saturated soil compared to that of the saturated

sand (2,875 ohm-cm compared to 50,500 ohm-cm) provides a possible cur-

rent path between all portions of the channel periphery through the

saturated soil and wood to the grounding point and essentially

V P

25

w - - - -

"fshort-circuits" any developed streaming potential. A second possible

cause of measurement failure lies within the electrochemical behavior of

clay minerals, specifically that generated streaming potentials are pos-

itive in sign and thus opposite to those generated in silica aggregates.

The loess soil used in the model contains 10-15 percent clay; water was

observed to flow macroscopically out of the soil and is assumed to also

flow microscopically in the pore spaces of the soil. The addition of

positive clay-generated streaming potentials to negative sand-generated

streaming potentials effectively could degrade measurements completely.

Plastic Tube (Pipe) Flow Model

43. Because of failure to control water flow in a satisfactory

way and to measure meaningful streaming potentials in the large above-

ground parallelepiped model a test cell was fabricated from PVC plastic

pipe as described in paragraph 26. The granular flow media was packed

into the cylindrical cell, densified by impact, electrodes inserted, and

the cell was sealed and attached to the same head and tailwater eleva-

tion controls as for the larger test. The test cell consistently al-

lowed control of the pressure gradient to within 0.01 ft over its

2-1/2-ft length. The discharge rates varied uncontrollably twice in the

entire sequence of testing due to clogging of the filter cloth at the

discharge and twice because incomplete densification prior to flow ini-

tiation caused a longitudinal void to develop during flow of water. The

tests in which discharge rates varied uncontrollably were each recon-

structed and performed again.

44. Temperature measurements were made in the discharged water

S during each test for use in determining the dielectric constant varia-

tion and the water density variation. The temperature extremes measured

were a low of 17*C and a high of 30.5*C. Corresponding values of the

dielectric constant are 81.47 and 76.58 (an inverse linear variation of

U 6 percent). Corresponding variations of water density were from

0.9988 g/cm 3to 0.9955 g/cm 3(an inverse nonlinear variation of0.3 percent). Both corrections for temperature-induced variations were

included in the ensuing data reduction.

26

45. The resistivity of the water used In the tests was expected

to vary both with changes in temperature and with changes in the munici-

pal water treatment. The temperature dependence of an aqueous electro--I

lyte is stated as (Keller and Frischknecht 1966):

Pt 0 7t 1 +0.025 (t - t0 )(7

where

Pt resistivity at the ambient temperature, t (ohm-cm)

Pt resistivity at a reference temperature, to (ohm-cm)

t - ambient temperature (deg C)

t - reference temperature (deg C)0

Variations in the electrical resistivity of the tap water used for the

streaming potential tests were essentially uncontrollable but could be

monitored periodically through each test. The method was to use the

plastic flow test cell as a resistivity measurement cell. The elec-

trodes implanted in the cell and aggregate for measuring streaming po-

tential were used as electrical resistance measurement electrodes alter-

nately with their primary function. To convert electrical resistance -

measurements between the electrodes into fluid resistivity data a cell

constant was determined by use of the unit resistivity cell described in

paragraph 42. Tap water at 20*C was placed in the unit cell and the re-

sistivity measured. Clean sand was then packed into the unit cell as

firmly as possible and the resistivity of the tap water saturated sand

measured to provide an adjustment factor for relating fluid resistivity

* to fluid-saturated sand resistivity. Sand from the same source was then

packed into the flow model cell to the same degree of firmness as in theWunit resistivity cell, determined by finger penetration effort. The

* flow model cell was then saturated with 20*C water by means of the fab-

ricated controlled-headwater supply. An electrical resistance measure-

ment across the imbedded electrodes was then made. Because the manual

compaction of the aggregate into the flow model cell in all further

tests was made as similar in effort as possible and because the physical

configuration of the flow model cell was not altered, it was assumed

27

that any variations in measured electrical resistance were directly pro-

portional to changes in the fluid resistivity. Incorporating both the

water-to-saturated sand resistivity cell factor and the resistivity

cell-to-flow model cell factor, the empirical relationship

P =0.163 R (8)fi

where

R = measured electrical resistance (ohms)

was used for all further fluid resistivity determinations.

46. Figure 7 is a plot of all calculated fluid resistivities ver- usus temperature. The points are grouped according to the day of testing

in which the data were obtained. Also included is a plot based on

Equation 7 using 20*C and 5300 ohm-cm as the reference temperature and

fluid resistivity, respectively. There is a slight tendency for the re- U

sistivity versus temperature data to follow the theoretical curve, but

the scatter is extreme among different days of testing. Variations in

the ion content of the tap water from day to day of the magnitude indi-

cated by the resistivity changes are possible within the standards of

the Public Health Service. The resistivity extremes of about 1500-

6000 ohm-cm observed can be interpreted (OCE 1979) as caused by a dis-

solved ion content range of 75-350 mg/1 equivalents of NaCl. The maxi-

mum desired content of chloride in drinking water is 250 mg/l and of S

total dissolved solids is 500 mg/l (Bouwer 1978). The final conclusion

was that fluid electrical resistivity varied to such a degree that the

streaming potential measurements had to be directly coupled to resistiv-

* ity measurements and temperature corrections were of relatively much S

less importance.

47. Flow media tested for streaming potential were:

a. Washed concrete sand (primarily quartz).

b. Washed pea gravel (primarily silica chert). w

c. Washed crushed limestone sand.

d. Washed limestone gravel.

e. Washed concrete sand over loess soil.

28

. . . . . . - _ S

The washed concrete sand medium was as described in paragraphs 18 and 39

for the large parallelepiped model as was the washed pea gravel (para-

graphs 18 and 38). The limestone sand was crushed and wet-sieved spe-

cifically for the present test series. It was packed into the flow

model cell in the same manner as the concrete sand. The limestone grav-

el was obtained from a bulk stockpile called "crushed limestone rock"

and washed prior to placing in the flow model cell. To examine the con-

ditions in the earlier large parallelepiped model which failed, the fi-

nal test in the tubular cell consisted of a compacted layer of loess

soil placed longitudinally with the remaining 25 percent of the circular

cross section filled with compacted concrete sand.

48. Tabulated results of the above described tests are presented

in Tables 1-5. Plots of measured streaming potentials versus water

pressure differential are presented in Figures 8-12. Calculations were

made to determine the electric surface potential (zeta potential) for

each measurement. Those surface potentials are plotted versus water

flow rate in Figures 13-17.

49. The plots of streaming potential, AE sp, versus applied

differential pressure, P , show that little direct variation in stream-V

ing potential was observed as related to changes in pressure. In any

* given series of measurements with a particular flow medium in one direc-

* tion the measured streaming potential was essentially constant as pres-

sure changed. In all the measurements taken as a whole the streaming

potential varied between -200 my and -360 my with a range of differen-

tial pressure variation between 39 cm of water and 108 cm of water.

50. The plots of surface potential, ;so versus volume flow rate,

Q , show relationships that appear to be hyperbolic with one asymptote

parallel to an upper constant surface potential value that is character-

istic of the flow media and the other asymptote parallel to a low magni-

tude constant volume flow rate. The data were not, however, adequately

controlled to justify regression to empirical equations relating surface

potential to flow rate.

29

S -- R- - ' ' " . . . . .. " . . •. . .

PART IV: CONCLUSIONS AND RECOMMENDATIONS

Conclusions

51. This study of modeling electrokinesis phenomena by measuring

electrical streaming potentials in realistic geologic media has produced

a number of observations that do not agree with past studies of lp

electrokinesis. The conclusion reached early in the activities of fab-

ricating flow models using naturally occurring granular and soil mate-

rials was that composite models for confined flow channels are difficult

to assemble with sufficient control to allow precise electrokinetic

measurements. Specific problems were identified as the inability to

establish and maintain a uniform flow of water, the imperfect confine-

ment of the water within the aggregate channels both hydraulically and

mechanically, and the impossibility of electrically isolating the flow-

ing water from the surrounding clay-bearing soil.

52. Despite recommendations of earlier investigators that the

only type of electrode appropriate to measure stzeaming potentials was a

low self-polarizing porous pot electrode, it was found in this study

that inert metal (silver) electrodes were far more stable electrically

than were the specially fabricated porous pot electrodes. The use of

metallic electrodes has also proven to be successful in field applica-

tions by the EEGD independently of this study. In addition to demon-

strated electrical stability the metallic electrodes were found to be

more economical to fabricate and are more durable.

53. Electrical potentials were measured in the modeled systems of

water flowing through porous media. Electrical potentials measured in

media that included water at rest were of much lower magnitude (-250 mv

compared to +3 my) and were interpreted as being electrical "noise."

Therefore, the measured electrical potentials in flowing water are in-

terpreted as successful detection of the electrokinetic phenomenon, de-

spite the poor correlation with the theoretical predictions of Equation 1

and other investigators. No correlation of streaming potential data to

the lithology of the aggregate in the flow channels was found. All

30

w - - -- - - - - - -

measured streaming potentials were negative in electrical sign and were

of reasonable magnitudes, but they showed insufficient variation because

of applied pressure differential to justify direct comparison to the

theoretical relationships as determined under controlled laboratory

conditions. The magnitude of streaming potentials was strongly influ-

enced by the electrical resistivity of the water used. The effect of

resistivity was stronger than could be accounted for by temperature

changes. Variations in the dissolved ionic content of the water were

* determined to be the primary uncontrolled variable. Both the dielectric

* constant and the viscosity of the water vary with temperature and play a

part in influencing streaming potential magnitudes but to a substan-

tially lesser degree than the chemistry effect of dissolved ions does by

way of electrical fluid resistivity.

54. To accommodate uncontrolled electrical resistivity varia-

tions, measurements of resistivity were made in conjunction with mesa-

urements of streaming potential. Thus variations in the grain surface

potential during water flow could be determined by calculation. The

surface potential was found to vary by an approximate hyperbolic rela-

* tionship with measured volume flow rates. The surface potential was

found to be in the range from -0.5 to -2.5 volts for quartz sand and

sand over soil, between -1.0 and -3.0 volts for limestone sand, between

* -2.0 and -2.5 volts for limestone gravel, and between -2.0 and

-6.5 volts for silica chert pea gravel. A relationship between surface

potential and volume flow rate has not previously been described in the

literature, though regular variations in surface po; :ential caused by

duration of flow have been described by Mandal (1969).

Recommendations

55. Further studies defining electrokinetic phenomena and devel-

oping streaming potential surveys should be performed in real geologicW

environments rather than modeled geologic conditions. Very close con-

trol on ancillary measurements of electrical resistivity, temperature,

and flow conditions will be required in such field studies, but model

31

fabrications such as described herein incorporate too many compromises

with reality to be satisfactory for simulating actual geologic

conditions.

56. Future streaming potential surveys should be used strictly on

a developmental basis until there is a better understanding of the fac-

tors controlling streaming potentials. Temperature effects are rela-

tively easy to Incorporate in streaming potential data reduction as they

affect the dielectric constant, the viscosity, and to some degree the -

fluid resistivity. However, two variables, fluid resistivity as con-

trolled by dissolved ion concentrations and the grain surface potential,

demonstrated large unanticipated variations in this study to the extent

that measured streaming potentials were largely uncorrelatable.

Frequent and accurate fluid resistivity measurements are required for

future quantitative applications of streaming potential surveys.

57. Metallic electrodes were found to be acceptable for measuring

U electrical potentials in earth materials during this study. Ibrous pot -

11nonpolarizable" electrodes were found to be unsatisfactory. Previous

investigations, with the exception of work by the EEGD, predict exactly

the opposite comparative success between the two types of electrode.

Further study is recommended to determine the most appropriate electrode

type for streaming potential measurements and to explain the reasons for

successful use of metallic electrodes in streaming potential studies by

the WES.

58. The unexpected observed relationship of grain surface poten-

tial with volume flow rate deserves future close attention for two

reasons. First, the variability of surface potential adds one more un-

* known to the quantitative interpretation of streaming potential data.

U Second, the volume flow rate is related by the flow medium microscopic

geometry to the intergranular flow velocity. Verification of the de-

pendence of surface potential on volume flow rate or, by inference, on

flow velocity could then make possible the use of streaming potential

data to calculate flow velocities in situ rather than be used only as an

indicator of the existence of flow or as a differential head measurement

technique. That verification is strongly recommended on both a theoret-

ical and experimental basis.

32

U -.

REFERENCES

Bates, E. R. 1973. "Detection of Subsurface Cavities," MiscellaneousPaper S-73-40, U. S. Army Engineer Waterways Experiment Station, CE,Vicksburg, Miss.

Bernstein, F., and Scala, C. 1959. "Some Aspects of the StreamingPotential and the Electrochemical SP in Shales," Petroleum Transactionsof the American Institute of Mining Engineers, Vol 216, pp 465-468.

Bogoslovosky, V. A., and Ogilvy, A. A. 1970. "Natural Potential Anoma-lies As a Quantitative Index of the Rate of Seepage From Water Reser-voirs," Geophysical Prospecting, Vol 18, No. 2, pp 261-268.

Bouwer, H. 1978. Groundwater Hydrology, McGraw-Hill, New York.

Bull, H. B., and Gortner, R. A. 1932. "Electrokinetic Potentials. X.The Effect of Particle Size on the Potential," Journal of PhysicalChemistry, Vol 36, No. 3, pp 111-119.

Butler, D. K., Llopis, J. L., Koester, J. P., and Kean, T. B. 1981."Geophysical Surveys, Clearwater Dam, Missouri," Unpublished Report,Geotechnical Laboratory, U. S. Army Engineer Waterways ExperimentStation, CE, Vicksburg, Miss.

Cooper, S., Koester, J. P., and Franklin, A. G. 1982. "GeophysicalInvestigations at Gathright Dam," Miscellaneous Paper GL-82-2, U. S.Army Engineer Waterways Experiment Station, CE, Vicksburg, Miss.

Corson, D., and Lorraine, P. 1962. Introduction to ElectromagneticFields and Waves, W. H. Freeman and Company, San Francisco.

Department of the Army, Office, Chief of Engineers. 1979. "GeophysicalExploration," Engineer Manual 1110-2-1802, Washington, D. C.

Gondouin, M., and Scala, C. 1958. "Streaming Potential and the SPLog," Journal of Petroleum Technology.

Helmholtz, H. Von. 1951. Annales Physik, No. 3:1879, GesammelteAbhandlugen, Vol 1, 1882, Transl. P. E. Bocquet, "Two Monographs ofElectrokinetics," Eng. Res. Publ. No. 33, University of Michigan,Ann Arbor.

Jakosky, J. J. 1950. Exploration Geophysics, Trija Publishing Company,Los Angeles, Calif.

Keller, G. V., and Frischknecht, F. C. 1966. Electrical Methods inGeophysical Prospecting, Pergamon Press, New York.

33

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Mandal, T. C. 1969. An Electrokinetic Study of Incrustation and Corro-

sion of Water Well Screen, M.S. Thesis, University of Nebraska, Lincoln,Nebr.

Mandal, T. C., and Edwards, D. M. 1971. "The Effects of Electrokinet-ics Upon Incrustation in Water Wells," Transactions of the AmericanSociety of Civil Engineers, Vol 14, No. 3.

Ogilvy, A. A., Ayed, M. A., and Bogoslovsky, V. A. 1969. "GeophysicalStudies of Water Leakages From Reservoirs," Geophysical Prospecting, -.Vol 17, No. 1, pp 36-62.

Saucier, R. T. 1970. "Geoelectrical Survey Performance and Evaluation,Walter F. George Reservoir, Alabama-Georgia," Miscellaneous PaperS-70-17, U. S. Army Engineer Waterways Experiment Station, CE,Vicksburg, Miss. 1

Schriever, W., and Bleil, C. E. 1957. "Streaming Potential in Spheri-cally Grained Sands," Journal of the Petrochemical Society, pp 170-175.

Smoluchowski, M. Von. 1951. Electrisch and Streaming Strom Handbuchde Electrizitat und des Magnetismers, Graetz (ed.), Vol II, P. E. -uBocquet, "Two Monographs of Electrokinetics," Eng. Res. Publ. No. 33,University of Michigan, Ann Arbor.

Weast, R. C., Selby, S. M., and Hodgman, C. D. 1965. Handbook of Chem-istry and Physics, The Chemical Rubber Company, Cleveland, Ohio.

Wyllie, M. R. J. 1951. "An Investigation of the Electrokinetic Compo-nent of the Self Potential Curve," Transactions of American Institute ofMining Engineers, Vol 192, pp 1-18.

Ii ..U

p

Table I

Tubular Cell Streaming Potential Measurements, Quartz Sand

Volume Streaming SurfacePressure Flow Fluid Potential, Fbtentia1,

*Differential, R-5te, Temperature, Resistivity, negative negativecm water cm sec degC kilohm-cm millivolts volts

Flow to Right

108.30 0.556 25.5 3.831 323.5 1.150101.44 0.488 27.0 3.749 307.5 1.20294.58 0.445 25.5 3.831 338.0 1.37687.72 0.393 26.0 3.831 328.5 1.44680.86 0.336 26.0 3.831 322.5 1.54074.01 0.245 19.0 4.320 325.0 1.45467.15 0.195 20.0 4.156 324.5 1.67160.29 0.153 19.5 4.059 335.0 1.96253.43 0.109 20.0 4.059 341.0 2.259

Flow to Left

108.30 0.654 23.0 5.738 241.5 0.566101.44 0.589 24.0 5.705 225.5 0.57194.58 0.520 25.0 5.705 218.5 0.59687.72 0.462 24.5 5.705 216.5 0.63580.86 0.433 25.0 5.738 203.0 0.64474.01 0.369 26.0 5.738 206.5 0.71967.15 0.308 26.0 5.738 207.5 0.79660.29 0.254 26.5 5.738 247.0 1.05953.43 0.201 27.0 5.738 244.0 1.18339.72 0.117 27.0 5.705 251.0 1.646

W

Table 2

Tubular Cell Streaming Potential Measurements, Pea Gravel

Volume Streaming SurfacePressure Flow Fluid Potential, Potential,

Differential, Rite, Temperature, Resistivity, negative negativecm water cm sec deg C kilohm-cm millivolts volts

Flow to Right

108.30 45.58 24.0 1.695 304.5 2.430101.44 42.47 24.0 1.695 285.0 2.42894.58 38.42 24.5 1.663 258.0 2.40687.72 34.85 24.5 1.663 260.5 2.620 u80.86 28.19 26.5 1.597 270.0 3.09974.01 25.64 26.0 1.597 261.5 3.27267.15 21.99 27.0 1.581 284.0 3.-7860.29 18.87 26.0 1.581 295.5 4.58553.43 14.22 23.0 1.646 249.5 4.13639.72 17.97 23.0 1.646 248.0 5.530 s

Flow to Left

108.30 39.87 24.0 1.614 291.0 2.439101.44 37.71 24.0 1.614 295.5 2.64494.58 35.23 24.0 1.614 289.0 2.77487.72 32.39 25.0 1.614 276.5 2.87580.86 30.18 25.0 1.597 289.5 3.30074.01 27.75 26.0 1.597 287.5 3.59867.15 25.42 26.0 1.597 285.0 3.93160.29 22.53 26.0 1.597 275.5 4.23253.43 19.31 26.0 1.597 275.0 4.767 S39.72 13.34 26.0 1.597 282.5 6.587

S S

V VW- ------ ----

Table 3

Tubular Cell Streaming Potential Measurements, Limestone Sand

Volume Streaming SurfacePressure Flow Fluid Potential, Potential,

Differential, Rite, Temperature, Resistivity, negative negativecm water cm sec deg C kilohm-cm millivolts volts

Flow to Right

108.30 6.54 24.0 3.260 266.5 1.106101.44 5.95 24.0 3.260 357.5 1.58494.58 5.32 24.0 3.260 353.0 1.67787.72 4.87 24.0 3.260 259.0 1.32780.86 4.32 25.0 3.340 260.0 1.41774.01 3.66 25.0 3.340 258.0 1.53667.15 3.14 25.0 3.340 259.0 1.70060.29 2.72 25.5 3.420 258.5 1.84953.43 2.27 26.0 3.420 260.5 2.10939.72 1.60 26.0 3.420 261.0 2.842

Flow to Left

108.30 5.36 26.0 3.100 312.0 1.374101.44 4.70 26.0 3.160 282.0 1.30194.58 4.20 26.0 3.160 283.5 1.40387.72 3.72 28.0 3.160 282.0 1.52080.86 3.34 28.0 3.210 283.5 1.63274.01 2.59 26.0 3.340 303.5 1.81667.15 2.26 27.0 3.340 320.5 2.125

- -- - - - - -- -- - - - -

U -0

Table 4

Tubular Cell Streaming Potential Measurements, Limestone Gravel

Volume Streaming SurfacePressure Flow Fluid Potential, Potential,

Differential, Rite, Temperature, Resistivity, negative negativecm water cm sec deg C kilohm-cm millivolts volts

Flow to Right

108.30 67.52 28.0 1.712 280.0 2.256101.44 55.85 29.5 1.712 246.0 2.13194.58 37.63 30.5 1.712 241.0 2.251108.30 39.33 29.0 1.760 279.0 2.197101.44 33.07 29.0 1.760 255.0 2.144

* •

.5

Table 5

Tubular Cell Streaming Potential Measurements, Sand Over Soil

Volume Streaming SurfacePressure Flaw Fluid Ptential, Pbtential,

Differential, Rite, Temperature, Resistivity, negative negativecm water cm sec deg C kilohm-cm millivolts volts

Flaw to Right

108.30 0.131 24.0 4.972 238.0 0.647101.44 0.122 24.5 4.890 211.0 0.62594.58 0.112 24.0 4.890 218.5 0.69287.72 0.103 24.0 4.890 218.0 0.74680.86 0.094 24.0 4.890 217.5 0.80574.01 0.084 24.0 4.890 241.5 0.97761.15 0.068 17.0 5.298 329.5 1.31260.29 0.062 17.0 5.379 302.0 1.31953.43 0.055 17.0 5.379 292.5 1.44239.72 0.041 18.0 5.281 273.0 1.851

Flaw to Left

108.30 0.135 20.0 4.075 302.0 0.984101.44 0.125 20.0 4.075 298.0 1.03594.58 0.115 20.0 4.075 308.0 1.149p87.72 0.104 20.0 4.108 317.5 1.26780.86 0.095 20.0 4.108 321.5 1.39174.01 0.084 21.0 4.026 307.0 1.48867.15 0.075 21.0 4.026 311.0 1.66160.29 0.056 21.5 3.994 298.0 1.79153.43 0.048 22.0 3.994 303.5 2.06439.72 0.031 23.0 3.928 290.5 2.715

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k--.

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40 60 80 100 120

Differential Pressure, P , centimetres of water

w Figure 9. Streaming potential versus differentialpressure, chert pea gravel medium-

: "4

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40 60 80 l00 120

Differential Pressure, P , centimetres of water

Figure 10. Streaming potential versus differential

. pressure, limestone sand medium

- -- P

1

S -S

-200

-220

-240 o

0

5 -260 -

-280

0

-300

-320

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•-340 Flow to Left

40 60 80 100 120

Differential Pressure, P , centime2tres of water

Figure 11. Streaming potential versus differentialpressure, limestone gravel medium

V S

-200

-220

- 240 0L-2

-28

0

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-30

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0.0 0.2 0.4 0,6

Volume Flow Rte, Q ,cubic centimetres per second ..

Figure 13. Surface potential versus volume flow

rate, quartz sand medium

- P

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0.10 20 30 40

Volume Flow Rate, Q ,cubic centimetres per second

Figure 14. Surface potential versus volume flow W

rate, chert pea gravel medium ....

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Volume Flow Rate, Q ,cubic centimetres per second

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w U

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rate, limestone gravel medium

b! .

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Figure 17. Surface potential versus volume flowrate, sand over soil media

*w p

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U -o

In accordance with letter from DAEN-RDC, DAEN-ASJ dated22 July 1977, Subject: Facsimile Catalog Cards forLaboratory Technical Publications, a facsimile catalog -card in Library of Congress MARC format is reproducedbelow.

Warriner, James B.Modeling of electrokinesis / by James B. Warriner, 1

P.A. Taylor (Geotechnical Laboratory, U.S. Army EngineerWaterways Experiment Station). -- Vicksburg, Miss. : TheStation ; Springfield, Va. ; available from NTIS, 1982.

34, (22] p. : ill. ; 27 cm. -- (Miscellaneous paperGL-82-13)Cover title."September 1982." -wFinal report.

'1 "Prepared for Assistant Secretary of the Army (RID),Department of the Army under ILIR Project No. 4AI61101A91D,Task A2, Work Unit 141."Bibliography: p. 33-34.

1. Electrokinetics. 2. Groundwater flow. 3. Geologicalmodeling. 4. Mathematical models. 5. Water--Electrical - V

properties. I. Taylor, P.A. II. United States.Assistant Secretary of the Army (R&D). II. U.S. Army

Warriner, James B.Modeling of electrokinesis / by James B. Warriner ... 1982

(Card 2)

Engineer Waterways Experiment Station. GeotechnicalLaboratory. IV. Title V. Series: Miscellaneous paper(U.S. Army Engineer Waterways Experiment Station) ; GL-82-13.TA7.W34m no.GL-82-13

i"V

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